The present invention relates to a recording apparatus having a recording electrode and a drum, which are disposed with a predetermined small clearance therebetween, and capable of forming a visible image or electrostatic image on an image supporting member by applying signals, corresponding to image information to be recorded, on the recording electrode.
The apparatus can be classified into a direct recording type and an electrostatic recording type.
In the direct recording type apparatus, a donor drum whose surface is covered uniformly to conductive magnetic toner is disposed in close proximity with a recording electrode with a predetermined clearance therebetween. A recording sheet is caused to pass through the clearance. Simultaneously, signals, signals corresponding to image information, are applied to the recording electrode and the donor drum is rotated while retaining the predetermined clearance, whereby the image corresponding to the image information is recorded on the recording sheet.
In in the electrostatic recording apparatus, the surface of a dielectric drum is uniformly charged and signals, corresponding to image information to be recorded, are applied to a recording electrode. The recording electrode is disposed in close proximity with the dielectric drum with a predetermined clearance therebetween, so that the charges on the surface of the dielectric drum are neutralized, in accordance with the applied signals, to form a latent electrostatic image corresponding to the image information. The latent electrostatic image is developed with toner and the toner image is then transferred to a recording sheet.
Conventionally, in the direct recording apparatus, the small clearance between the recording electrode and the donor drum is maintained by a mechanism in which support shafts are projected from the opposite ends of the recording electrode. Guide rollers, rotatably attached to the respective support shafts through bearings, contact cylindrical guide rails on the opposite sides of the donor drum. Precise maintenance of the close or small clearance is important in the sense that when the clearance is too small, the recording paper contacts with the surface of the donor drum and toner adheres to the recording paper, resulting in the smearing of the background of the recording paper. On the other hand, when the clearance is too great, toner is not attracted to the surface of the recording paper due to the loss of electrical energy within the clearance. Furthermore, when the clearance changes either regularly or irregularly, the density of recorded image changes, resulting in the reduction of image quality.
Therefore, it is required that the small clearance between the donor drum and the recording electrode be maintained constant along the axial direction of the drum.
However, if the bearings or the guide rollers are eccentric in the above-mentioned conventional direct recording apparatus, the clearance between the donor drum and the recording electrode is directly changed by the eccentric distance, and the change of the clearance as great as 5.mu. in inevitable even if any precision bearings are employed.
The conventional electrostatic recording apparatus has the same limitations, with respect to the clearance, as that of the conventional direct recording apparatus.